In steel reinforced concrete construction, there are generally three types of splices or connections; namely lap splices; mechanical splices; and welding. Probably the most common is the lap splice where two bar ends are lapped side-by-side and wire tied together. The bar ends are of course axially offset which creates design problems, and eccentric loading whether compressive or tensile from bar-to-bar. Welding is suitable for some bar steels but not for others and the heat may actually weaken some bars. Done correctly, it requires great skill and is expensive. Mechanical splices normally require a bar end preparation or treatment such as threading, upsetting or both. They also may require careful torquing. Such mechanical splices don't necessarily have high compressive and tensile strength, nor can they necessarily qualify as a Type 2 mechanical high fatigue strength connection.
Accordingly, it would be desirable to have a high strength coupler which will qualify as a Type 2 coupler permitted anywhere in a structure in all four earthquake zones of the United States, and yet which is easy to assemble and join in the field and which does not require bar end preparation or torquing in the assembly process. It would also be desirable to have a coupler which could be assembled initially simply by sticking a bar end in an end of a coupler sleeve or by placing a coupler sleeve on a bar end.